Various devices have been used to minimize turbulent flow in duct systems so that accurate flow measurements can be made. Most of these include honeycomb-type straightening sections oriented axially with the duct and bulk airflow to straighten the otherwise turbulent flow pattern. These straightening sections must be placed in adequately long, straight runs of duct or conduit which frequently are not available in modern air conditioning duct work. Typical of prior art arrangements are the flow measuring stations disclosed in U.S. Pat. Nos. 3,685,355 and 3,733,900 issued to Kenneth W. DeBaun; U.S. Pat. No. 3,981,183 issued to Roger T. Goulet; and U.S. Pat. No. 4,297,900 issued to Robert O. Brandt. All use honeycomb-type flow straightening means in combination with a pitot tube array that measures air velocity by separately sensing static and total pressure in a traverse downstream of the honeycomb.
Even where the airflow has been straightened, it frequently does not have an equalized profile across the duct so that it is necessary to take a large number of velocity samples across the duct in order to get a true average value of velocity and, thus, an accurate determination of the quantity of airflow. Profiling of the airflow pattern to equalize it across the duct sometimes has been accomplished by shaped honeycomb sections such as is illustrated in U.S. Pat. No. 3,964,519 issued to Kenneth W. DeBaun.